1. Field of the Invention
This invention relates to an integrated circuit fabrication process in which a laser radiant energy beam is employed for the purpose of trimming one or more elements of the circuit. More particularly, it relates to such a process in which special steps are taken to protect circuit elements not to be trimmed from damage by a laser radiant energy beam used to trim other elements of the circuit, and to the protection structure so produced.
2. Description of the Prior Art
The use of a laser for trimming both active and passive devices in an integrated circuit is known in the art. For example, Johnson, commonly assigned application Ser. No. 830,979, filed Sept. 6, 1977, discloses the use of a laser for trimming a region in a semiconductor substrate forming a part of a transistor. That application also points out that it is known to use a laser for trimming thick and thin film resistors, as well as for severing shorting links.
While such uses of laser radiant energy beams have proved to be successful for accomplishing their intended purpose, care must be taken to avoid having the laser beam contact other portions of the integrated circuit not to be trimmed. Inability to maintain close enough control over the laser beam to avoid contacting circuit elements not to be trimmed has proved to be a significant yield detractor in the fabrication of laser trimmed circuits, particularly under high volume automated process conditions. A need therefore remains for improvement of processes for laser trimming of integrated circuits.